THE RIPENING OF CREAM. iO 
numbers a large one, the proportionate difference is very much 
jess than in the unripened cream; one sample of unripened 
cream, for instance, containing two hundred and twenty times 
as many bacteria as another sample, while the largest number 
in the ripened cream was only about eleven times as great as 
the smallestenumber. 
The only conclusions of any significance from these facts are 
that the cream received by creameries is in various stages of 
ripening, and secondly, that the number of bacteria in ripened 
cream does not run much over 500 million per cubic centimeter. 
In the well ripened cream this number is rarely surpassed. 
INCREASE OF ACID PRODUCING ORGANISMS. 
The next problem was to determine the proportion of species 
producing acid to those not producing acid. This determina- 
tion is quite easy by the use of the. litmus gelatin, in all cases 
where liquefying organisms are not present in great abundance. 
If the plates are allowed to grow for three or four days every 
acid producing organism is easily determined by its being sur- 
rounded by a red halo where the litmus has been changed by the 
acid. Itis avery easy matter to go over the series of plates 
and thus determine the proportion of bacteria producing an 
acid reaction. The results of about twenty-five experiments 
in regard to this problem are shown in the following table. 
This table includes only results with cream from two cream- 
eries, the results with cream from the private dairies being 
given on a later page. | 
It will be noticed from Table 4 that in most cases the per- 
centage of acid organisms increased during the ripening. In 
the unripened cream the percentage of acid organisms is quite 
variable. The lowest percentage given in the table is 66. 
From 66 per cent. the proportion of acid organisms varies to 
as high as 100 per cent. in a single specimen. In most cases 
the percentage of lactic organisms in the unripened cream is 
over 95 per cent., and not infrequently as high as 99 per 
cent. 
The ripened cream; on the other hand, shows uniformly a 
higher percentage of acid organisms. In each of the experi- 
ments (with one exception) given in the table the number of 
acid organisms is over 97 per cent.; in all but four it is over 99 
